U.S. patent application number 11/922726 was filed with the patent office on 2009-07-09 for conducting fluid containing millimetric magnetic particles.
Invention is credited to Jean Chevalet, Emmanuelle Dubois.
Application Number | 20090173907 11/922726 |
Document ID | / |
Family ID | 35976780 |
Filed Date | 2009-07-09 |
United States Patent
Application |
20090173907 |
Kind Code |
A1 |
Dubois; Emmanuelle ; et
al. |
July 9, 2009 |
Conducting Fluid Containing Millimetric Magnetic Particles
Abstract
The invention relates to a composite material formed by
millimeter-scale particles of magnetic material A and a conductive
liquid B. The material is characterized in that the material A is
chosen from magnetic compounds and magnetic alloys and is in the
form of particles, the mean size of which is between 0.1 and 2 mm,
and in that the support fluid B is a conductive fluid chosen from
metals, metal alloys and salts that are liquid at temperatures
below the Curie temperature of the material A, or from mixtures
thereof.
Inventors: |
Dubois; Emmanuelle; (Paris,
FR) ; Chevalet; Jean; (Ivry sur Seine, FR) |
Correspondence
Address: |
CROWELL & MORING LLP;INTELLECTUAL PROPERTY GROUP
P.O. BOX 14300
WASHINGTON
DC
20044-4300
US
|
Family ID: |
35976780 |
Appl. No.: |
11/922726 |
Filed: |
June 26, 2006 |
PCT Filed: |
June 26, 2006 |
PCT NO: |
PCT/FR2006/001469 |
371 Date: |
January 16, 2009 |
Current U.S.
Class: |
252/62.55 ;
205/334 |
Current CPC
Class: |
Y02E 30/40 20130101;
Y02E 30/30 20130101; H01F 1/442 20130101; G21C 15/28 20130101; C09K
5/12 20130101 |
Class at
Publication: |
252/62.55 ;
205/334 |
International
Class: |
C09K 5/00 20060101
C09K005/00; C25B 1/00 20060101 C25B001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 27, 2005 |
FR |
0506509 |
Claims
1. A composite material comprising a magnetic material A and a
liquid support B, wherein: the material A is selected from the
group consisting of magnetic compounds and magnetic alloys and is
in the form of particles, the mean diameter of which is between 0.1
and 2 mm; and the support fluid B is a conductive fluid selected
from the group consisting of metals, metal alloys salts that are
liquids at temperatures below the Curie temperature of the material
A, and from mixtures thereof.
2. The composite material as claimed in claim 1, wherein the
electrically conductive fluid B is a metal that is a liquid by
itself or is a mixture of several metals that are liquids at
temperatures below the Curie point of the magnetic material A with
which they are associated.
3. The composite material as claimed in claim 2, wherein the
electrically conductive fluid B is selected from the group
consisting of Hg, Ga, In, Sn, As, Sb, alkali metals, and mixtures
thereof.
4. The composite material as claimed in claim 1, wherein the
electrically conductive fluid B is a molten metal alloy selected
from the group consisting of In/Ga/As alloys, Ga/Sn/Zn alloys,
In/Bi alloys, Wood's alloy, Newton's alloy, Arcet's alloy,
Lichtenberg's alloy and Rose's alloy.
5. The composite material as claimed in claim 1, wherein the
electrically conductive fluid B is a salt selected from the group
consisting of: alkylammonium nitrates in which the alkyl group
comprises from 1 to 18 carbon atoms, guanidinium nitrates,
imidazolium nitrates and imidazolinium nitrates; alkali metal
chloroaluminates, which are liquids at temperatures above
150.degree. C.; and salts comprising a BF.sub.4.sup.-,
PF.sub.6.sup.- or trifluoroacetate anion and a cation chosen from
amidinium [RC(.dbd.NR.sub.2)--NR.sub.2].sup.+, guanidinium
[R.sub.2N--C(.dbd.NR.sub.2)--NR.sub.2].sup.+, pyridinium C1
##STR00005## imidazolium ##STR00006## imidazolinium ##STR00007##
and triazolium ##STR00008## ions, in which each substituent R
represents, independently of the others, H or an alkyl radical
having from 1 to 8 carbon atoms.
6. The composite material as claimed in claim 1, wherein the
magnetic material A is selected from the group consisting of
magnetic metals, metal oxides, magnetic alloys and magnetic
compounds.
7. The composite material as claimed in claim 6, wherein the
magnetic material A is selected from the group consisting of iron,
iron oxide, cobalt, nickel, steel and iron/silicon alloys.
8. The composite material as claimed in claim 1, wherein the amount
of magnetic particles is at most equal to the threshold value above
which the dispersion becomes a two-phase or solid dispersion.
9. The composite material as claimed in claim 1, wherein the
material A comprises substantially spherical particles.
10. The composite material as claimed in claim 1, which comprises
substantially spherical particles of magnetic material having a
means size between 0.1 and 2 mm and particles of magnetic material
the size distribution of which is homogeneous, between 1 nm and 50
.mu.m.
11. The composite material as claimed in claim 1, wherein the
magnetic material particles may be formed by a batch of a first
magnetic material A and by a batch of a second magnetic material A'
chosen from the group defined for A.
12. The material as claimed in claim 1, comprising a magnetic
material/electrically conductive fluid B pair selected from the
group consisting of Fe/Hg, steel/Hg, Co/Hg, Ni/Hg, Fe/Ga, steel/Ga,
Fe/Ga+Sn, and Fe/Wood's alloy.
13. A method for the preparation of a conductive ferrofluid
material comprising a magnetic material A and an electrically
conductive fluid B comprising introducing a precursor of the
magnetic material A into an electrically conductive fluid B, which
method is implemented electrochemically in an electrochemical cell
in which: the electrolyte comprises an ionically conductive medium
containing the precursor of the material A in the form of
particles, the mean diameter of which is between 0.1 and 2 mm; the
precursor of the material A is a nonionic precursor; the cathode
comprises a film of the conductive fluid B connected to a potential
source capable of delivering a current density between 100
mA/cm.sup.2 and 3 A/cm.sup.2; the anode comprises a material that
is nonoxidizable under the conditions of the method; and the
cathode is subjected to a negative potential difference relative to
the anode.
14. The method as claimed in claim 13, wherein the precursor of the
magnetic material A is selected from the group consisting of
magnetic metals, metal oxides, magnetic alloys and magnetic
compounds.
15. The method as claimed in claim 14, wherein the precursor is
selected from the group consisting of iron, iron oxide, cobalt,
nickel, steel and Fe--Si alloys.
16. The method as claimed in claim 13, wherein the precursor
particles are substantially spherical.
17. The method as claimed in claim 13, wherein the precursor
particles are in the form of a first batch formed from
substantially spherical particles having a mean size of between 0.1
and 2 mm and of a second batch formed from micron-scale particles,
the size distribution of which is homogeneous, between 1 nm and 50
.mu.m.
18. The method as claimed in claim 13, wherein the precursor
particles are formed by a batch of a precursor of a first magnetic
material A and by a batch of a precursor of a second magnetic
material A' chosen from the group defined for A.
19. The method as claimed in claim 13, wherein the respective
amounts of precursor of material A and of conductive fluid B are
such that the final concentration of particles of magnetic material
in the conductive fluid B remains less than the value above which
the dispersion becomes a two-phase or solid dispersion, taking into
account the degree of solubility of the material A in the fluid
B.
20. The method as claimed in claim 13, wherein the electrically
conductive fluid B is selected from the group consisting of metals,
metal alloys and salts that are liquids at temperatures below the
Curie temperature of the material A, and mixtures thereof.
21. The method as claimed in claim 20, wherein the electrically
conductive fluid B is a metal that is a liquid by itself or is a
mixture of several of them metals that are liquids at temperatures
below the Curie point of the magnetic material A with which they
are associated.
22. The method as claimed in claim 21, wherein the electrically
conductive fluid B is selected from the group consisting of Hg, Ga,
In, Sn, As, Sb, alkali metals, and mixtures thereof.
23. The method as claimed in claim 20, wherein the electrically
conductive fluid B is a molten metal alloy selected from the group
consisting of In/Ga/As alloys, Ga/Sn/Zn alloys, In/Bi alloys,
Wood's alloy, Newton's alloy, Arcet's alloy, Lichtenberg's alloy
and Rose's alloy.
24. The method as claimed in claim 20, wherein the electrically
conductive fluid B is a salt selected from the group consisting of:
alkylammonium nitrates in which the alkyl group comprises from 1 to
18 carbon atoms, guanidinium nitrates, imidazolium nitrates and
imidazolinium nitrates; alkali metal chloroaluminates, which are
liquids at temperatures above 150.degree. C.; and salts comprising
a BF.sub.4.sup.-, PF.sub.6.sup.- or trifluoroacetate anion and a
cation chosen from amidinium [RC(.dbd.NR.sub.2)--NR.sub.2].sup.+,
guanidinium [R.sub.2N--C(.dbd.NR.sub.2)--NR.sub.2].sup.+,
pyridinium ##STR00009## imidazolium ##STR00010## imidazolinium
##STR00011## and triazolium ##STR00012## ions, in which each
substituent R represents, independently of the others, H or an
alkyl radical having from 1 to 8 carbon atoms.
25. The method as claimed in claim 21, wherein one or more elements
are added to the metal forming the electrically conductive fluid B,
which elements may form a stable liquid phase or a liquid amalgam
when said metal is mercury.
26. The method as claimed in claim 13, wherein the ionically
conductive medium is formed by a solution of a nonoxidizing acid or
of a strong base in a solvent.
27. The method as claimed in claim 26, wherein the solvent is
selected from the group consisting of water, polar organic liquids
and molten salts.
Description
[0001] The present invention relates to a composite material formed
by particles of magnetic material and a conductive liquid.
BACKGROUND OF THE INVENTION
[0002] It is known to use heat-transfer fluids in refrigeration or
heating systems, in particular in heat exchangers in industrial
plants, such as those of nuclear power stations or solar energy
converters.
[0003] Heat-transfer fluids generally consist of liquid chemical
compounds or mixtures of these compounds, such as ethylene glycol,
propylene glycol, petroleum-based oils, or silicones. Mention may
also be made of mixtures of heavy polyaromatic compounds, aryl
ethers, and terphenyls, which are particularly resistant to high
temperatures and allow operation up to about 300.degree. C. It is
also known to use certain organic molten salts containing
particulate additives as heat-transfer fluid. Such materials can be
used over a wide temperature range, and the purpose of the
particulate additives is to improve the thermal conductivity. The
fluids are generally made to circulate by mechanical systems,
comprising moving parts, especially blades and pumps. These
mechanical systems undergo wear owing in particular to the friction
caused by the passage of the heat-transfer fluid. Furthermore, when
they are used at temperatures above about 350.degree. C., these
fluids undergo extensive rapid degradation and cause vapor pressure
problems. Their use in the field of high-power high-temperature
heat exchangers for example is therefore excluded.
SUMMARY OF THE INVENTION
[0004] The object of the present invention is to provide a material
capable of serving as a heat-transfer fluid that overcomes the
drawbacks of the systems of the prior art, namely the wear of
mechanical parts, and that increases the maximum use
temperature.
[0005] This is why the subject of the present invention is a
composite material, a method of producing it, and its
applications.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0006] The composite material according to the present invention is
formed by a support fluid B and particles of magnetic material A.
Said composite is characterized in that: [0007] the material A is
chosen from magnetic compounds and magnetic alloys and is in the
form of particles, the mean diameter of which is between 0.1 and 2
mm; and [0008] the support fluid B is a conductive fluid chosen
from metals, metal alloys and salts that are liquids at
temperatures below the Curie temperature of the material A, or from
mixtures thereof.
[0009] A material according to the invention has a high electrical
conductivity and a high thermal conductivity, and, although
heterogeneous, it may remain stable owing to the good wetting of A
by B when the densities are close.
[0010] The magnetic material A may be chosen from magnetic metals
and metal oxides, magnetic alloys and magnetic components. Among
metals and metal oxides, mention may be made of iron, iron oxide,
cobalt and nickel. Among alloys, mention may be made of steel and
alloys having a high magnetic permeability. An alloy having a high
magnetic permeability is an alloy having an initial permeability of
greater than 1000. Such alloys are described in particular in
Chapter 2 of the work "Alliages magnetiques et ferrites", [Magnetic
alloys and ferrites] by M. G. Say, published by Dunod, Paris, 1956.
As examples of high-permeability alloys, mention may in particular
be made of iron-silicon alloys and alloys consisting essentially of
Ni and Fe, sold under the name Mu-metal.RTM. or Permalloy.RTM..
Amorphous magnetic alloys may also be mentioned, such as for
example alloys of Fe, Co and Ni containing about 20% B, C, Si or P,
and nanocrystalline magnetic alloys, such as for example
Fe/Cu/Nb/Si/B alloys and Fe/Zr/B/Cu alloys.
[0011] The material A may consist of substantially spherical
particles having a mean diameter between 0.1 and 2 mm. The material
A may also be in the form of two batches: a first batch formed from
substantially spherical particles having a mean size between 0.1
and 2 mm; a second batch formed from micron-scale particles, the
size distribution of which is homogeneous, for example between 1 nm
and 50 .mu.m. The particles of magnetic material may furthermore
consist of a batch of a first magnetic material A and a batch of a
second magnetic material A' chosen from the group defined for
A.
[0012] The term "electrically conductive fluid" is understood to
mean a fluid that has an electrical resistivity of less than about
1000 ohms per centimeter within the temperature range in which the
electrolysis takes place.
[0013] When the electrically conductive fluid B is a metal, it may
be chosen from metals that are liquids by themselves or in the form
of mixtures of several of them at temperatures below the Curie
point of the magnetic material A with which they are associated. As
examples, mention may be made of Hg, Ga, In, Sn, As, Sb, alkali
metals and mixtures thereof.
[0014] When the electrically conductive fluid B is a molten metal
alloy, it may be especially chosen from In/Ga/As alloys, Ga/Sn/Zn
alloys, In/Bi alloys, Wood's alloy, Newton's alloy, Arcet's alloy,
Lichtenberg's alloy and Rose's alloy. Some of these alloys are
commercially available. The composition and the melting point of
some of them are given below:
TABLE-US-00001 Composition (% by weight) T.sub.m(.degree. C.)
21.5In--62.5Ga--16.0Sn 10.7 17.6In--69.8Ga--12.5Sn 10.8
82.0Ga--12.0Sn--6.0Zn 17 67In--33Bi 70 Wood's alloy:
50Bi--25Pb--12.5Sn--12.5Cd 70 Newton's alloy: 50Bi--31.2Pb--18.8Sn
97 Arcet's alloy: 50 Bi, 25Sn--25Pb 98 Lichtenberg's alloy:
50Bi--20Sn--30Pb 100 Rose's alloy: 50Bi--22Sn--28Pb 109
[0015] As examples of salts that may constitute the conductive
fluid B mention may be made of: [0016] alkylammonium nitrates in
which the alkyl group comprises from 1 to 18 carbon atoms,
guanidinium nitrates, imidazolium nitrates and imidazolinium
nitrates; [0017] alkali metal chloroaluminates, which are liquids
at temperatures above 150.degree. C.; and [0018] salts comprising a
BF.sub.4.sup.-, PF.sub.6.sup.- or trifluoroacetate anion and a
cation chosen from amidinium [RC(.dbd.NR.sub.2)--NR.sub.2].sup.+,
guanidinium [R.sub.2N--C(.dbd.NR.sub.2)--NR.sub.2].sup.+,
pyridinium
##STR00001##
[0018] imidazolium
##STR00002##
imidazolinium
##STR00003##
and triazolium
##STR00004##
ions, in which each substituent R represents, independently of the
others, H or an alkyl radical having from 1 to 8 carbon atoms, said
salts having conductivities of up to 10 mS/cm and being very
stable. As an example, mention may be made of
1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide.
[0019] Among composite materials according to the invention,
mention may in particular be made of the materials consisting of
the following elements: steel balls/Hg, steel balls/Ga, steel
balls+Fe powder/Hg, steel balls+Fe powder/Ga.
[0020] Another subject of the present invention is a method for
producing the composite material. Said method consists in
introducing a precursor of the magnetic material A into an
electrically conductive fluid B, which method is implemented
electrochemically in an electrochemical cell in which: [0021] the
electrolyte consists of an ionically conductive medium containing
the precursor of material A in the form of particles, the mean
diameter of which is between 1 and 10 .mu.m; [0022] the precursor
of the material A is a nonionic precursor in solution; [0023] the
cathode consists of a film of the conductive fluid B connected to a
potential source capable of delivering a current density between
100 mA/cm.sup.2 and 3 A/cm.sup.2; [0024] the anode consists of a
material that is nonoxidizable under the conditions of the method,
for example platinum or vitreous carbon; and [0025] the cathode is
subjected to a negative potential difference relative to the
anode.
[0026] The electrolysis may either be current-controlled, by
controlling the variation in potential at the cathode, or
potential-controlled, by controlling the potential relative to a
reference electrode (using a control device of the potentiostat
type). The potential applied to the cathode must in all cases be
the most negative possible in order to reduce the interfacial
tension between the materials A and B, but it must be limited so as
not to induce other electrochemical reactions such as the excessive
evolution of hydrogen or the formation of amalgams, detrimental to
the efficiency and to the stability of the product.
[0027] The anode may be placed in a compartment separated from the
cathode by a porous wall. The cell furthermore includes a reference
electrode when the electrolysis is potential-controlled.
[0028] The nonionic precursor in solution of the magnetic material
A may be chosen from metals and metal oxides, and also from the
abovementioned alloys.
[0029] The precursor is introduced in the form of particles into
the ionically conductive medium forming the electrolyte, said
particles preferably being substantially spherical. In one
particular embodiment, the precursor is in the form of balls having
a heterogeneous size distribution. In another embodiment, the
precursor of the magnetic material is introduced in the form of two
batches: a first batch formed from substantially spherical
particles having a mean size between 0.1 and 2 mm; a second batch
formed from micron-scale particles, the size distribution of which
is homogeneous, for example between 1 nm and 50 .mu.m. The
precursor particles may furthermore be formed by a batch of a
precursor of a first magnetic material A and by a batch of a
precursor of a second magnetic material A' chosen from the group
defined for A.
[0030] The respective amounts of precursor of the material A and of
conductive fluid B are such that the final particle concentration
of magnetic material in the conductive fluid B remains below the
value above which the dispersion becomes a two-phase or solid
dispersion, which would result in precipitation, taking into
account the degree of solubility of A in B. The determination of
this value lies within the competence of a person skilled in the
art.
[0031] The precursor particles may be used as defined above but
they may also be used after they have been coated with a metal
having an affinity for A in the conductive fluid B.
[0032] The conductive fluid B used for preparing the composite
material according to the invention is chosen from the conductive
fluids defined above for the material itself.
[0033] When the electrically conductive fluid B consists of a given
metal, one or more elements may be added to it which may form a
stable liquid phase (or a liquid amalgam when said metal is
mercury) and which stabilize the dispersion of the particles A
within the conductive fluid, preventing them from aggregating. For
example, if B is mercury, Sn, Ag, Cu, Cd, Zn, Tl, Pb, In, As or Sb
may be added to it in a proportion that remains less than the value
that would lead to the formation of a solid phase.
[0034] The presence of impurities is liable to significantly modify
the interfacial properties between the magnetic material A and the
conductive fluid B, and consequently the wettability of the
material A by the conductive fluid B. If by implementing the method
of the invention for a given pair A/B a suitable result is not
obtained, it is recommended to check the nature and the level of
impurities.
[0035] The method of the present invention may be implemented in
particular for preparing a composite material having magnetic
properties and electrical and thermal conduction properties from
the precursors and the electrically conductive fluids mentioned
above. It is particularly useful for preparing a composite material
in which the material constituting the magnetic particles A and the
material constituting the electrically conductive fluid B exhibit
little or no mutual affinity, and when the magnetic material is at
best only weakly wettable by the electrically conductive fluid. As
examples of such materials, mention may be made of the conductive
ferrofluid materials containing the following elements:
TABLE-US-00002 Fe and/or steel particles in Hg Fe and/or steel
particles in Ga Co or Ni particles in Hg Fe particles in Ga + Sn Fe
particles in Wood's alloy Mu-metal .RTM. particles in Wood's
alloy.
[0036] The precursor particles of A may be introduced into the
ionically conductive medium and then into the electrically
conductive liquid B during the electrolysis, that is to say
gradually until the desired concentration in B is obtained. In this
case, the current density and/or the potential are modified at the
same time as the precursor of A is introduced, thereby making it
possible, as the case may be, to introduce precursor particles of
A' that are different from the precursor particles of A.
[0037] The ionically conductive medium is preferably a nonoxidizing
medium. It may be formed by a solution of a nonoxidizing acid (for
example HCl) or of a strong base in a solvent. The solvent may be
water, a polar organic liquid or a molten salt. The polar organic
liquid may be chosen from acetonitrile, acetone, dimethylformamide
(DMF), dimethylsulfoxide (DMSO), propylene carbonate (PC), dimethyl
carbonate and N-methylpyrrolidone. The molten salt may be chosen
from those defined above as electrically conductive fluid.
[0038] The potential source to which the cathode is connected must
be capable of delivering a current density of at least around 100
mA/cm.sup.2 of cathode.
[0039] When the electrochemical cell is potential-controlled, it
necessarily includes a reference electrode, and the potential
differential difference between the cathode and said reference
electrode is fixed within a range such that the interfacial tension
between A and B is reduced so as to allow wetting of the particles
A by the liquid B. For example, when the particles A are Fe
particles and the liquid B is Hg, the voltage is between -1 V and
-3 V relative to the reference electrode.
[0040] When the electrochemical cell operates in galvanostatic
mode, that is to say when it is current-controlled, and when it
includes a reference electrode, it is necessary to impose action
thresholds that reduce the current so that the potential difference
between the cathode and the reference electrode is limited to the
range defined in the case in which the cell is
potential-controlled.
[0041] When the electrochemical cell is current-controlled without
a control device and when it does not include a reference
electrode, it is necessary to monitor the total potential relative
to a predetermined limit, for example using a temporary reference
electrode.
[0042] In practice, when operating in current-controlled mode, it
is preferable to use an electrochemical cell that includes a
reference electrode.
[0043] In a particularly preferred way of implementing the
electrochemical preparation, a magnetic field is applied
perpendicular to the plane of the cathode, so as to subtract the
magnetic particles A formed from the region of the
electrolyte/cathode interface, in order to control the rate of
their growth during the initial phases of their formation. In
another method of implementation, other types of action on the
material undergoing synthesis may be obtained by superposing pulses
or AC components on the current or potential controlling the
process, in the absence or in the presence of said perpendicular
magnetic field.
[0044] At the end of the operation, the conductive fluid
constituting the cathode is highly enriched with magnetic particles
A and constitutes the electrically conductive ferrofluid material
of the invention.
[0045] A third subject of the invention is the use of the composite
material as heat-transfer fluid. The presence of magnetic particles
allows the material to move inside tubes in which it is supposed to
circulate by a simple induction effect, thereby obviating the need
for mechanical parts subject to wear. Furthermore the metallic
nature of this of this electrically conductive support fluid and
its higher thermal conduction than that of the usual fluids (even
when doped with metal particles) promote heat transfer.
[0046] The present invention is illustrated below by a few specific
exemplary embodiments to which however the invention is not
limited.
[0047] The following starting products were used in the
examples:
[0048] Mercury
[0049] Gallium
[0050] 100C6 steel balls (made of iron with 1% carbon and 1%
chromium) with a diameter of 1.5 mm
[0051] Powdered iron, sold under the reference 312-31 (reduced iron
for analysis) by Riedel-de Haen, consisting of spherical particles
having a diameter of about 10 .mu.m
[0052] Mu-metal.RTM..
[0053] The materials were prepared in an electrochemical cell which
was connected to a potential source and provided with stirring
means, and in which the cathode was formed by a layer of the
electrically conductive fluid B, a platinum electrode provided the
contact with the cathode, a second platinum electrode operated as
anode, and a calomel electrode operated as reference electrode.
Example 1
Iron/Steel/Hg Ferrofluid Material
Preparation of the Material:
[0054] 8.694 g of mercury (material B) were placed in the bottom of
the cell, 10 ml of 0.1M HCl were added and the mixture was heated
to 50.degree. C. The potential source generated a potential
difference of 6 V between the two platinum electrodes, inducing a
current of around 250 mA. Next, 0.2 g of steel balls and 0.54 g of
powdered iron were added. The layer of mercury was subjected to
slight stirring to make it easier to incorporate the magnetic
materials in the mercury layer and to prevent coarsening of the
hydrogen bubbles at the surface of the mercury.
Characterization of the Material Obtained:
[0055] The volume fraction of iron in the material obtained was
0.127.
[0056] The measured saturation magnetization of this material was
250 kA/m.
[0057] The initial susceptibility at low magnetic field was
1.45.
Example 2
Iron/Steel/Ga Ferrofluid Material
Preparation of the Material:
[0058] 4.86 g of gallium (material B) were placed in the bottom of
the cell and 10 ml of 0.2M HCl were added. The mixture was heated
to a temperature of 50.degree. C. and then a potential difference
of 11 V was applied between the two platinum electrodes. Next, 0.2
g of steel balls and 0.142 g of iron powder were added. A magnet
was then used to bring the iron beneath the gallium, which was
subjected to slight stirring using the magnet.
Characterization of the Material Obtained:
[0059] The volume fraction of iron in the material obtained was
0.04.
[0060] The measured saturation magnetization of this material was
72 kA/m.
[0061] The initial susceptibility at low magnetic field was
0.42.
Example 3
Mu-Metal/Wood's Alloy Ferrofluid Material
Preparation of the Material:
[0062] 6.1 g of Wood's alloy (material B) were placed in the bottom
of the cell and 10 ml of 0.1M HCl were added. The mixture was
heated to a temperature of 75.degree. C. and then a potential
difference of 6 V was applied between the two platinum electrodes.
Next, 0.32 g of Mu-metal in the form of platelets measuring 1
mm.times.1 mm.times.0.05 mm were added in 3 fractions, the
additions being spaced apart by 5 minutes. After each addition, the
potential difference between the two electrodes was raised to 12 V
for 30 s.
Characterization of the Material Obtained:
[0063] The volume fraction of magnetic material in the material
obtained was around 0.08.
[0064] The saturation magnetization of the material was 110
kA/m.
[0065] The initial susceptibility at low magnetic field was
3.5.
* * * * *